java并发：AtomicInteger 以及CAS无锁算法【转载】

package automic;
 
public class AtomicIntegerTest extends Thread{
 
    private Integer count=0;
    @Override
    public void run() {
        for(int i=1;i<=500;i++){
            count++;
        }
         System.out.println("count的值是："+ count);
 
    }
 
    public static void main(String[] args) {
        AtomicIntegerTest a=new AtomicIntegerTest();
            Thread t1 = new Thread(a);
            Thread t2 = new Thread(a);
            t1.start();
            t2.start();
           
    }
 
}

package automic;
 
import java.util.concurrent.atomic.AtomicInteger;
 
public 
class AtomicIntegerTest2 extends Thread{
    /**
     * 这里使用了AtomicInteger类，这是一个对于变量可以进行原子性操作的类；核心是CAS无锁算法;
     * 下面两个构造器其中一个进行了值得初始化
     * public AtomicInteger(int initialValue) {
     *   value = initialValue;
     * }
     * public AtomicInteger() {
     * }
     */
 
    
    private AtomicInteger count=new AtomicInteger(0);
    @Override
    public void run() {
        for(int i=1;i<=500;i++){
            /**
             * getAndIncrement是以原子的方式给当前值加1
             */
            count.getAndIncrement();
        }
         System.out.println("count的值是："+ count);
 
    }
 
    public static void main(String[] args) {
        AtomicIntegerTest2 a=new AtomicIntegerTest2();
            Thread t1 = new Thread(a);
            Thread t2 = new Thread(a);
            t1.start();
            t2.start();
           
    }
 
}

public class AtomicInteger extends Number implements java.io.Serializable {
    private static final long serialVersionUID = 6214790243416807050L;
 
    // setup to use Unsafe.compareAndSwapInt for updates
    private static final Unsafe unsafe = Unsafe.getUnsafe();
    private static final long valueOffset;
}

 static {
        try {
            valueOffset = unsafe.objectFieldOffset
                (AtomicInteger.class.getDeclaredField("value"));
        } catch (Exception ex) { throw new Error(ex); }
    }

 public final int getAndIncrement() {
        for (;;) {
            int current = get();
            int next = current + 1;
            if (compareAndSet(current, next))
                return current;
        }
    }

public final int getAndIncrement() {
        return unsafe.getAndAddInt(this, valueOffset, 1);
 }

    /**
     * set()方法 ,设置一个值
     */
    public final void set(int newValue) {
        value = newValue;
    }
 
    /**
     * lazySet()方法，没有storeload屏障的set,出现于JDK1.6
     */
    public final void lazySet(int newValue) {
        unsafe.putOrderedInt(this, valueOffset, newValue);
    }
 
    /**
     * getAndSet()方法 原子性的获取并且设置值
     */
    public final int getAndSet(int newValue) {
        return unsafe.getAndSetInt(this, valueOffset, newValue);
    }
 
    /**
     * 如果当前值和内存值相等，那么进行更新
     */
    public final boolean compareAndSet(int expect, int update) {
        return unsafe.compareAndSwapInt(this, valueOffset, expect, update);
    }
 
    /**
     * weak的CAS，也就是没有volatile语义的CAS，没有加入内存屏障
     */
    public final boolean weakCompareAndSet(int expect, int update) {
        return unsafe.compareAndSwapInt(this, valueOffset, expect, update);
    }
 
    /**
     * 自增加，返回原来的值.
     */
    public final int getAndIncrement() {
        return unsafe.getAndAddInt(this, valueOffset, 1);
    }
 
    /**
     * 自减少，返回原来的值
     */
    public final int getAndDecrement() {
        return unsafe.getAndAddInt(this, valueOffset, -1);
    }
 
    /**
     * 原子性的增加delta的值
     */
    public final int getAndAdd(int delta) {
        return unsafe.getAndAddInt(this, valueOffset, delta);
    }
 
    /**
     * 自增1
     */
    public final int incrementAndGet() {
        return unsafe.getAndAddInt(this, valueOffset, 1) + 1;
    }
 
    /**
     * 自减1
     */
    public final int decrementAndGet() {
        return unsafe.getAndAddInt(this, valueOffset, -1) - 1;
    }
 
   
    /**
     * 阻塞式更新，并且对prev进行一个IntUnaryOperator操作运算
     */
    public final int updateAndGet(IntUnaryOperator updateFunction) {
        int prev, next;
        do {
            prev = get();
            next = updateFunction.applyAsInt(prev);
        } while (!compareAndSet(prev, next));
        return next;
    }
 
    /**
     * 阻塞式更新，并对prev和x，进行二元运算操作。于jdk1.8出现
     */
    public final int getAndAccumulate(int x,
                                      IntBinaryOperator accumulatorFunction) {
        int prev, next;
        do {
            prev = get();
            next = accumulatorFunction.applyAsInt(prev, x);
        } while (!compareAndSet(prev, next));
        return prev;
    }